1. Field of the Invention
This invention relates to a safety circuit for an electronic flash and, more particularly, to a safety circuit for eliminating any danger of shock or injury in the event that the cover from an electronic flash should be removed.
2. Description of the Prior Art
Electronic flash units typically employ large capacitors for storing electrical energy that is used for firing a flashtube. A DC-to-DC converter circuit which is energized from a low voltage battery typically in the order of 6 volts charges the storage capacitor in a known manner to a high voltage generally above 300 volts. If a flash unit user should either deliberately or accidentally remove the cover from the flash unit and thereafter contact the terminals of the charged storage capacitor, discharge current from the capacitor could produce serious injury.
It is well known in the art for electronic flash units to include a safety circuit for discharging the storage capacitor to protect users against injury. One such safety circuit is disclosed in U.S. Pat. No. 3,969,737, entitled "Electronic Flash Unit for Cameras Adapted to Receive Flashbulbs", by E. Kendrick, issued July 13, 1976, and shows an electronic flash unit having a circuit, the sole purpose of which is to discharge the storage capacitor to prevent accidental injury to the user. Circuits of this type generally include a normally open switch in series with a bleeder resistor, the switch and resistor being connected parallel to the main storage capacitor. The switch is closed automatically whenever the housing of the flash unit is opened thereby discharging the storage capacitor through the switch and the resistor. Although circuits of this type have been found to operate reliably, the bleeder resistor must be able to handle the high discharge current from the storage capacitor; and, since the resistor is required solely as a safety feature, it introduces an additional complexity and cost to the flash unit.
Other safety circuits for discharging storage capacitors in electronic flashes have utilized the quench tube in a quench strobe in place of an additional bleeder resistor as is fully described in U.S. Pat. No. 4,204,140, entitled "Safety Circuit for Electronic Flash Apparatus", by R. Willis, issued May 20, 1980. Although the safety circuit of the Willis patent eliminates the need for providing an additional bleeder resistor, it is nevertheless only applicable to electronic flash units of the quench type, and would not be applicable to electronic flash units of the non-quench type.
Therefore, it is a primary object of this invention to provide a safety circuit for discharging the main storage capacitor in an electronic flash of either the quench or non-quench type without utilizing any additional components other than a safety switch.
It is a further object of this invention to provide a safety circuit for discharging the storage capacitor in an electronic flash of either the quench or the non-quench type without providing an additional bleeder resistor.
Other objects of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the mechanism and system possessing the construction, the combination of elements and the arrangement of parts which are exemplified in the following detailed disclosure.